Most Ezreal guides I've read recommend maxing Mystic Shot(Q) first but recently I see a lot of progamers and high ELO players max his Essence Flux(W) first after getting the token point in Mystic Shot(Q) and Arcane Shift(E). However, I still see other high end players max Mystic Shot(Q) first, too.
After checking up on the exact values of the skills I see Essence Flux(W) having better scaling base damage at a higher Mana cost as well as having the advantage of the attack speed buff/debuff scaling with level.
His Mystic Shot(Q) gets a shorter cooldown at the cost of higher mana cost with lower damage increase than Essence Flux(W).
Is it always better to max Essence Flux(W) first or does it depend on specific situations in which it is better to max one over the other?
Note: I only mean AD Ezreal, not AP Ezreal and with a build like Boots->Phage->Sheen->Trinity